JPH05150735A - Active matrix type liquid crystal display device - Google Patents

Abstract

PURPOSE:To greatly reduce variation in contrast or brightness due to a difference in viewing angle by gradually varying voltage-transmissivity characteristics from the upper part to the lower part of a panel according to the viewing angle. CONSTITUTION:The voltage-transmissivity characteristics of the same liquid crystal material depend upon the panel temperature, the panel gap, the tilt angle of an oriented, film, the rubbing intersection angle, the sticking angle of a polarizing plate, and auxiliary capacity. It is, however, difficult to continuously vary the panel gap, rubbing intersection angle, and polarizing plate sticking angle as to processes. Even when the amplitude of a picture element driving voltage applied to a liquid crystal layer is decreased from the upper part to the lower part of the panel, the voltage-transmissivity characteristics when respective places are viewed, approximates to the same shape. The panel temperature, the tilt angle of liquid crystal molecules, the value of the auxiliary capacity, and the amplitude of the picture element driving voltage are decreased from the upper part to the lower part of the panel to improve the visual angle dependency of optical characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a large active matrix type liquid crystal display device.

[0002]

2. Description of the Related Art Usually, a display mode of an active matrix type liquid crystal display device is a TN mode, and liquid crystal molecules are oriented in a 90-degree twist between two substrates. At this time, the orientations of liquid crystal molecules near the substrate interface are orthogonal to each other,
Right-handed or left-handed orientation is provided from one substrate side to the other substrate side.

The orientation of the liquid crystal molecules is imparted by rubbing the alignment film, and the rubbing direction determines the viewing angle azimuth at which the maximum contrast is obtained (this direction is defined as the main viewing angle direction).

In the conventional liquid crystal display device, the optical design is such that the main viewing angle direction is above the panel or below the panel. Therefore, the viewing angle characteristics of a normal liquid crystal display device show symmetrical characteristics on the left and right sides of the panel, but show asymmetrical optical characteristics on the upper and lower sides of the panel. In particular, the asymmetry of the optical characteristics in the vertical direction of the panel is remarkable in the normally white mode in which white display is performed when no voltage is applied.

[0005]

By the way, although the panel size is gradually increasing due to the progress of the liquid crystal display technology, when the panel size is adapted to the workstation, the angle of looking at the panel is the upper part of the panel and the panel. Since there is a large difference between the lower part and the same content, there arises a problem that the contrast and the brightness level are significantly different between the upper part of the panel and the lower part of the panel.

Therefore, an object of the present invention is to provide an active matrix type liquid crystal display device which can solve the above problems.

[0007]

In order to solve the above problems, the active matrix type liquid crystal display device of the present invention is
A liquid crystal display device in which the orientation of the liquid crystal is restricted so that the viewing angle direction in which the maximum contrast is obtained is above the panel has at least one or more of the following features.

That is, (1) the magnitude of the amplitude of the pixel driving voltage is gradually reduced from the upper part of the panel to the lower part, and (2) the panel temperature of the upper part of the panel is equal to or higher than the panel temperature of the lower part of the panel. (3) The tilt angle of the liquid crystal molecules gradually decreases from the upper part of the panel to the lower part of the panel, and (4) the magnitude of the auxiliary capacitance gradually decreases from the upper part of the panel to the lower part of the panel.

[0009]

The reason why the above configuration is adopted will be described below. By the way, even if the same contents are displayed, the contrast and the brightness level are greatly different between the upper panel and the lower panel because the angle of viewing the panel is different between the upper panel and the lower panel.

Now, a liquid crystal display screen having a length of 250 mm from the upper end to the lower end of the panel display section is displayed on the panel center normal line 300.
In a liquid crystal display device in which the orientation of the liquid crystal is restricted so that the main viewing angle direction is above the panel when the screen is viewed from a distance of mm, the upper part of the panel is θ = 22.6 degrees, and ψ =
The image will be viewed with a tilt of 0 degree, and the lower part of the panel will be viewed in the main viewing angle direction, θ = −22.6 degrees, and ψ = 180 degrees.

The viewing angle (θ, ψ) is defined as shown in FIG. However, θ when viewed from the front is positive, and θ when viewed from above is negative. Further, in detail, the contrast or the brightness is different between the upper and lower parts of the panel because the viewing angle dependence of the voltage-transmittance characteristic is different in each part. FIG. 4 shows the viewing angle dependence of a typical voltage-transmittance characteristic of a liquid crystal display device in which the alignment direction of the liquid crystal is restricted so that the main viewing angle direction is above the panel. Now, when the panel is viewed from a distance of 300 mm on the normal to the center of the panel, the upper part of the panel shows the voltage-transmittance characteristic of FIG. 4A, and FIG. 4B shows the voltage-transmittance characteristic of the lower part of the panel. .. If these two curves are approximated to the same type, the problem of the difference in the viewing angle characteristics can be eliminated. 4C shows the voltage-transmittance characteristic when viewed from directly above the center of the panel, and FIG. 4D shows the voltage-transmittance characteristic when viewed from the right side of the panel.

The voltage-transmittance characteristic of the same liquid crystal material depends on the panel temperature, the panel gap, the tilt angle of the alignment film, the rubbing crossing angle, the laminating angle of the polarizing plate, and the size of the auxiliary capacitance. Therefore, by creating a panel in which these conditions change from the upper part of the panel to the lower part of the panel, the viewing angle dependence of the optical characteristics can be improved. However, among the above items, it is difficult and not practical to continuously change the panel gap, the rubbing crossing angle, and the bonding angle of the polarizing plate in the process.

On the other hand, the same can be said from the driving method. That is, even when the amplitude of the pixel drive voltage applied to the liquid crystal layer is reduced from the upper part of the panel to the lower part of the panel, the voltage-transmittance characteristics when the respective parts are included are apparently the same. Approach.

Therefore, the viewing angle dependence of the optical characteristics can be improved by decreasing the panel temperature, the tilt angle of the liquid crystal molecules, the size of the auxiliary capacitance, or the amplitude of the pixel driving voltage from the upper part to the lower part of the panel. An active matrix type liquid crystal display device can be obtained.

[0015]

Embodiments of the active matrix type liquid crystal display device according to the present invention will be described below.

In each of the examples, in evaluating the panel characteristics due to the difference in the viewing angle to the panel, when the upper panel of a large panel (the display area is 250 mm × 320 mm) is estimated at θ = 22.6 degrees. And the voltage-transmittance characteristic when the lower part of the panel was observed at θ = −22.6 degrees, and the viewing angle dependence of the optical characteristic of the panel was evaluated.

First, the first embodiment will be described. The active matrix liquid crystal display device according to the first embodiment is a liquid crystal display device in which the orientation of the liquid crystal is restricted so that the viewing angle direction where the maximum contrast is obtained is above the panel. The size is gradually reduced from the top of the panel to the bottom.

More specifically, two glass substrates having an ITO electrode on the surface (effective display area 250 mm × 3)
20 mm) on top of which is a polyimide paint PSI manufactured by Chisso Corporation.
-201 (4.0 wt.%, NMP solution) is applied by a spin coating method and cured under the curing condition of 200 ° C. for 1 hour. Then, after rubbing at a twist angle of 90 degrees so that the main viewing angle direction is above the panel, these substrates are bonded together via a 4.0 μm glass fiber,
Liquid crystal ZLI-1565 manufactured by Merck Ltd. was enclosed to obtain a liquid crystal panel.

Next, as a comparative example, the viewing angle dependence of the voltage-transmittance characteristic of this liquid crystal panel was measured according to a conventional method. 2A and 2B show respective voltage-transmittance characteristics when the panel upper part and the panel lower part are viewed. These differences are θ = 22.6 degrees and θ =
This is a difference in voltage-transmittance characteristic at −22.6 degrees, and since the voltage value for obtaining the same transmittance is different, it seems that the panel characteristics are different between the upper part of the panel and the lower part of the panel.

Next, the driving voltages of the upper and lower parts of the panel were set as shown in [Table 1] so as to be uniformly changed from the upper part of the panel to the lower part of the panel.

[0021]

[Table 1]

The results of the transmittance are shown in FIGS. 1 (a) and 1 (b). FIG. 1A shows the upper part of the panel.
(B) shows the lower part of the panel, and the horizontal axis is (driving voltage-driving voltage amplitude lower limit) / (driving voltage amplitude upper limit-driving voltage amplitude lower limit).

According to the configuration of the first embodiment, almost the same light transmittance can be obtained even when the angles of viewing the panel upper portion or the panel lower portion are different, and the practical value thereof is extremely large.

Although the lower limit of the drive voltage amplitude range is changed according to the position in the panel in the first embodiment, it corresponds to the voltage at the white level in the normally white mode, and strict white level control is required. If not, the same voltage value may be set regardless of the position in the panel.

In the liquid crystal display device in which the alignment direction of the liquid crystal is regulated so that the viewing angle direction in which the maximum contrast is obtained is the upper side of the panel as in the first embodiment, from the upper part of the panel to the lower part of the panel, A more uniform display in the vertical direction can be achieved by gradually lowering the drive voltage applied to the liquid crystal layer in accordance with the viewing angle dependence of the voltage-transmittance characteristic. Further, as an effect accompanying the present invention, there is an effect of reducing the degree of black floating in the main viewing angle direction.

Next, the second embodiment will be described. In the second embodiment, the large-sized panel prepared in the first embodiment is used, and the upper part of the panel is 60 ° C. and the lower part of the panel is 2 ° C.
The backlight-inverter, transformer, drive circuit, fan, etc. are arranged so that the temperature is 0 ° C, the module is assembled, and the voltage-luminance characteristic when the panel upper part or the panel lower part is viewed from a distance of 300 mm on the panel center normal. Was evaluated.

The contrast at this time (ratio between the luminance when no voltage was applied and the luminance when a voltage of 6 V was applied) was measured and found to be 40 at the upper part of the panel and 50 at the lower part of the panel. On the other hand, as a comparative example, a module was designed such that the entire panel had a temperature of 20 ° C., and the contrast was measured in the same manner. As a result, it was 15 at the upper part of the panel and 40 at the lower part of the panel.

By designing the module so that the upper part of the panel has a higher temperature than the lower part of the panel, the viewing angle range of the panel can be further widened. The second embodiment is to provide a constant temperature distribution in the panel surface, which is extremely superior in construction method as compared with the conventional panel which attempts to make the temperature distribution in the panel surface as uniform as possible. It is advantageous.

Next, a third embodiment will be described. In the third embodiment, 2 having an ITO electrode on the surface is used.
One glass substrate (effective display area 250 mm x 320 m
m) was spin-coated to form a polyimide alignment film paint RN-753 manufactured by Nissan Chemical Industries, Ltd. so that the dry film thickness would be 600 angstroms. At this time, the curing temperature of the alignment film was controlled for 1 hour by controlling the surface temperature of the hot stage so that the upper portion of the substrate was 200 ° C. and the lower portion of the substrate was 170 ° C.

Then, after rubbing at a twist angle of 90 degrees so that the main viewing angle direction is above the panel, it is 4.5 μm.
These substrates were bonded to each other via the glass fiber of No. 3, and liquid crystal LIXON-5047 manufactured by Chisso Petrochemical was sealed therein to obtain a liquid crystal panel.

Next, in the same manner as in the second embodiment, the contrast was measured when the panel upper part and the panel lower part were observed from a distance of 300 mm on the panel center normal line. The results are shown in [Table 2].

[0032]

[Table 2]

As a comparative example, the inside of the substrate surface is all 1
A panel was prepared using a substrate cured at 70 ° C., and the same contrast as above was measured. The results are also shown in [Table 2].

The alignment film used in the third embodiment is 200
It has a tilt angle of 4.8 degrees when cured at 1 ° C for 1 hour.
It was confirmed in another experiment that a tilt angle of 3.3 ° C. was obtained in the curing treatment at 70 ° C. for 1 hour, and the tilt angle was increased from the upper part of the panel to the lower part of the panel as in the third embodiment. The effectiveness of changing from small to small is obvious.

In the third embodiment, the viewing angle dependence in the vertical direction can be greatly alleviated and the viewing angle can be widened, and its practical value is high. Next, a fourth embodiment will be described.

In the fourth embodiment, there are 1036800 trio pixels on a glass substrate, and each dot is a T pixel.
An array substrate having FT elements and a color filter substrate (effective display area 250 mm × 320 mm) having red, green and blue filters corresponding to the respective pixels are spin-coated on a Hitachi Chemical Co., Ltd. Made polyimide alignment film paint LX
-5400 was formed into a film having a dry film thickness of 600 angstroms. At this time, the alignment film was cured at a curing temperature of 170 ° C. At this time, from the upper part of the panel toward the lower part of the panel, an auxiliary capacitor having a capacity of 5 times the liquid crystal capacity in the upper part of the panel and a capacity of 1 times the liquid crystal capacity in the lower part of the panel was formed in the array substrate together with the TFT element.

After that, rubbing was performed at a twist angle of 90 degrees so that the main viewing angle direction was above the panel, and then 4.0 μm.
These substrates were bonded to each other through the glass fiber of No. 3, and liquid crystal ZLI-1565 manufactured by Merck Ltd. was enclosed to obtain a liquid crystal panel.

Then, by the same method as in the third embodiment,
When the upper and lower parts of the panel were observed from a distance of 300 mm on the normal to the center of the panel, the contrast was measured and found to be 37 at the upper part of the panel and 62 at the lower part of the panel.

As described above, by decreasing the size of the auxiliary capacitance from the upper part of the panel to the lower part of the panel, it is possible to greatly improve the difference in contrast and luminance characteristics due to the difference in panel viewing angle.

[0040]

As described above, according to each constitution of the present invention,
Since the voltage-transmittance characteristics are gradually changed from the upper part of the panel to the lower part of the panel according to the expected angle, the change in the contrast or the brightness based on the difference in the viewing angle looking at the upper part of the panel and the lower part of the panel is significantly changed. Can be relaxed.

[Brief description of drawings]

FIG. 1 is a diagram showing voltage-transmittance characteristics when a panel upper portion and a panel lower portion are viewed from a distance of 300 mm on a panel normal line in a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing voltage-transmittance characteristics of a normal liquid crystal display device as a comparative example in the first embodiment of the present invention.

FIG. 3 is a diagram for explaining the definition of a viewing angle.

FIG. 4 is a diagram showing the viewing angle dependence of voltage-transmittance characteristics for explaining the operation of the present invention.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Yuji Saya 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. In a liquid crystal display device in which the orientation of the liquid crystal is restricted so that the viewing angle direction in which the maximum contrast is obtained is above the panel, the amplitude of the pixel drive voltage is gradually increased from the upper part to the lower part of the panel. A miniaturized active matrix liquid crystal display device. 2. A liquid crystal display device in which the orientation of the liquid crystal is restricted so that the viewing angle direction in which the maximum contrast is obtained is above the panel, so that the panel temperature in the upper part of the panel is equal to or higher than the panel temperature in the lower part of the panel. Active matrix liquid crystal display device. 3. In a liquid crystal display device in which the orientation of the liquid crystal is restricted so that the viewing angle direction in which the maximum contrast is obtained is above the panel, the tilt angle of the liquid crystal molecules gradually decreases from the upper part of the panel to the lower part of the panel. Active matrix type liquid crystal display device. 4. In a liquid crystal display device in which the orientation of the liquid crystal is restricted so that the viewing angle direction in which the maximum contrast is obtained is above the panel, the size of the auxiliary capacitance gradually decreases from the upper part of the panel to the lower part of the panel. Active matrix type liquid crystal display device.